Re: [PATCH v5 1/6] kexec: move locking into do_kexec_load

From: ebiederm@xmission.com (Eric W. Biederman)
To: Arnd Bergmann <arnd@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	Helge Deller <deller@gmx.de>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	"David S. Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>,
	Feng Tang <feng.tang@intel.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
	linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-s390@vger.kernel.org, sparclinux@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH v5 1/6] kexec: move locking into do_kexec_load
Date: Wed, 28 Jul 2021 11:09:22 -0500	[thread overview]
Message-ID: <87eebifmj1.fsf@disp2133> (raw)
In-Reply-To: <20210727144859.4150043-2-arnd@kernel.org> (Arnd Bergmann's message of "Tue, 27 Jul 2021 16:48:54 +0200")

Arnd Bergmann <arnd@kernel.org> writes:

> From: Arnd Bergmann <arnd@arndb.de>
>
> The locking is the same between the native and compat version of
> sys_kexec_load(), so it can be done in the common implementation
> to reduce duplication.

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

>
> Co-developed-by: Eric Biederman <ebiederm@xmission.com>
> Co-developed-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  kernel/kexec.c | 44 ++++++++++++++++----------------------------
>  1 file changed, 16 insertions(+), 28 deletions(-)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index c82c6c06f051..9c7aef8f4bb6 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -110,6 +110,17 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>  	unsigned long i;
>  	int ret;
>  
> +	/*
> +	 * Because we write directly to the reserved memory region when loading
> +	 * crash kernels we need a mutex here to prevent multiple crash kernels
> +	 * from attempting to load simultaneously, and to prevent a crash kernel
> +	 * from loading over the top of a in use crash kernel.
> +	 *
> +	 * KISS: always take the mutex.
> +	 */
> +	if (!mutex_trylock(&kexec_mutex))
> +		return -EBUSY;
> +
>  	if (flags & KEXEC_ON_CRASH) {
>  		dest_image = &kexec_crash_image;
>  		if (kexec_crash_image)
> @@ -121,7 +132,8 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>  	if (nr_segments == 0) {
>  		/* Uninstall image */
>  		kimage_free(xchg(dest_image, NULL));
> -		return 0;
> +		ret = 0;
> +		goto out_unlock;
>  	}
>  	if (flags & KEXEC_ON_CRASH) {
>  		/*
> @@ -134,7 +146,7 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>  
>  	ret = kimage_alloc_init(&image, entry, nr_segments, segments, flags);
>  	if (ret)
> -		return ret;
> +		goto out_unlock;
>  
>  	if (flags & KEXEC_PRESERVE_CONTEXT)
>  		image->preserve_context = 1;
> @@ -171,6 +183,8 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>  		arch_kexec_protect_crashkres();
>  
>  	kimage_free(image);
> +out_unlock:
> +	mutex_unlock(&kexec_mutex);
>  	return ret;
>  }
>  
> @@ -247,21 +261,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
>  		((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))
>  		return -EINVAL;
>  
> -	/* Because we write directly to the reserved memory
> -	 * region when loading crash kernels we need a mutex here to
> -	 * prevent multiple crash  kernels from attempting to load
> -	 * simultaneously, and to prevent a crash kernel from loading
> -	 * over the top of a in use crash kernel.
> -	 *
> -	 * KISS: always take the mutex.
> -	 */
> -	if (!mutex_trylock(&kexec_mutex))
> -		return -EBUSY;
> -
>  	result = do_kexec_load(entry, nr_segments, segments, flags);
>  
> -	mutex_unlock(&kexec_mutex);
> -
>  	return result;
>  }
>  
> @@ -301,21 +302,8 @@ COMPAT_SYSCALL_DEFINE4(kexec_load, compat_ulong_t, entry,
>  			return -EFAULT;
>  	}
>  
> -	/* Because we write directly to the reserved memory
> -	 * region when loading crash kernels we need a mutex here to
> -	 * prevent multiple crash  kernels from attempting to load
> -	 * simultaneously, and to prevent a crash kernel from loading
> -	 * over the top of a in use crash kernel.
> -	 *
> -	 * KISS: always take the mutex.
> -	 */
> -	if (!mutex_trylock(&kexec_mutex))
> -		return -EBUSY;
> -
>  	result = do_kexec_load(entry, nr_segments, ksegments, flags);
>  
> -	mutex_unlock(&kexec_mutex);
> -
>  	return result;
>  }
>  #endif